Safe arm initiator

ABSTRACT

An initiator in which the igniter is separated from the output charge by a rotor of magnetic material. The rotor provides an ignition path between the igniter and the output charge only when the rotor is rotated into an armed position. The rotor is normally magnetically restrained in a safe position, and is rotated into its armed position by the application of an electrical arming signal to an electromagnetic coil acting upon the rotor.

United States Patent Allen [151 3,658,009 51 Apr. 25, 1972 [541 SAFE ARM INITIATOR [72] Inventor: Richard L. Allen, Saratoga, Calif.

[73] Assignee: Lockheed Aircraft Corporation, Burbank,

Calif.

[22] Filed:, May 8, 1969 [21] Appl. No.: 822,890

52 1 us. CI ..1o2/7o.2, 102/76 [51] int. Cl. ..F42b 5/08 [58] Field of Search 1 02/702 [56] References Cited UNITED STATES PATENTS 2,978,982 4/1961 Bianchi 102/702 A 3,500,747 3/1970 Parker ..l02/70.2

Primary Examiner-Samuel Feinberg Attorney-Paul F. Morgan and George C. Sullivan ABSTRACT An initiator in which the igniter is separated from the output charge by a rotor of magnetic material. The rotor provides an ignition path between the igniter and the output charge only when the rotor is rotated into an armed position. The rotor is normally magnetically restrained in a safe position, and is rotated into its armed position by the application of an electrical arming signal to an electromagnetic coil acting upon the rotor.

1 Claims, 4 Drawing Figures PATENIEnIPIIzs I972 3.658009 FIG. 1 FIG. 2

f 1? FIRE l2 ARM PERMIT ARM I"- Y I 3 3 FIRE Mm ARM FIRE ARM PERMIT RETuRN RETURN PERMIT RETURN O ARM IO [8 Fl G. Fl 4 INVENTOR.

RICHARD S. ALLEN Agent SAFE ARM INITIATOR The present invention relates to a safe/arm initiator in which positive mechanical interruption of the firing train is achieved by a simple electrical system utilizing an electromagnetically actuated rotor. A simple, reliable and miniaturized initiator which may be actuated by low voltage is provided.

The providing of a lightweight and highly reliable initiator is of great importance in the fields of explosives, pyrotechnics, propulsion systems and the like. Such igniters are often subjected to severe environmental conditions and forces, yet must ignite the desired charge with high reliability upon the firing command, and must positively insure against accidental or premature ignition through electrical or mechanical malfunctions. The size and weight of the initiator is critical in missiles and other projectiles, particularly where a large number of separate initiators are required. Low voltage initiators are preferable from a weight standpoint to the high voltage exploding bridge wire initiators presently in wide use, as the latter require a large and heavy electrical power supply arrangement. However the sensitivity of low voltage ignition charges necessitates a positive mechanical interruption of the ignition train from the igniter for absolute safety. Various complicated mechanically driven arrangements have been developed for interrupting the ignition train, some using rotors as shown for example in U.S. Pat. Nos. 2,915,013, 3,306,207, 3,311,058 and 2,978,982. These initiators require an external mechanical power source or, as in U.S. Pat. No. 2,978,982, the application of centrifugal forces. These prior arrangements are deficient in the light of the stringent requirements discussed above.

The initiator described herein may be completely sealed, requires only low voltage and low current arming and ignition signals, and is insensitive to environmental conditions or forces. It is highly suitable for miniaturized packaging in a selfcontained hermetic unit of less than 1 cubic inch weighing only a few ounces. It can be directly connected to provide reliable ignition of any desired charge.

Further objects, features and advantages of the invention pertain to the particular arrangement and structure whereby the above mentioned aspects of the invention are attained. The invention will be better understood by reference to the following discussion and to the drawings forming a part thereof, which are substantially proportional, wherein:

FIG. 1 is a central cross-sectional view of an exemplary embodiment of the invention;

FIG. 2 is a cross-sectional view taken along the line 2 2 of FIG. 1;

FIG. 3 is a cross-sectional view taken along the line 3 3 of FIG. 1; and

FIG. 4 is a schematic of the initiator embodiment of FIGS. l-3.

Referring to FIGS. 1 4, there is shown therein an exemplary safe/arm initiator in accordance with the present invention. The initiator 10 includes a housing 12 containing a magnetic rotor 14 and an igniter 16 mounted therein. There is an output charge 18 adjacent the rotor 14 and spaced from the igniter 16. The rotor 14 separates the igniter 16 from the output charge 18 to prevent ignition of the output charge by the igniter for any position of the rotor 14 other than an armed position. The rotor 14 has an ignition lead 20 extending therethrough. When the rotor is rotated into its armed position, the ignition lead 20 is interposed between the igniter l6 and the output charge 18 to complete the firing train. The rotor 14 is urged into and maintained in its safe position (shown in FIGS. 1-3) by the magnetic interaction of the rotor 14 with a magnetic shield 22. The rotor 14 is rotated into its armed position (as shown in FIG. 4) solely by the application of a low voltage arming signal to an electromagnetic coil 24 surrounding the rotor 14. The electromagnetic force provided by the coil 24 overcomes the permanent magnetic force urging the rotor 14 in its safe position.

Preferably the housing 12 is a rigid sealed container providing a complete hermetic seal for the entire initiator 10, in which all components thereof are enclosed. No mechanical shafts or the like extend through the housing 12. The only external connections are electrical circuits and the only mechanical movement is that of the rotor 14 itself, which is entirely inside the housing 12.

The igniter 16, or detonator, is shown here as having dual headers and dual bridge wires connecting with a single explosive column 26. This provides a dual electro-explosive interface for increased reliability. The igniter 16 is otherwise conventional and the explosive material can be lead styphanate, lead azide or other suitable material.

The rotor 14 is mounted to, and partially enclosed within, a support frame 28 of non-magnetic material fixed to the housing 12. The explosive column 26 of the igniter 16 is contained within the support frame 28 and opens only closely adjacent the outer surface of the rotor 14. This opening of the explosive column 26 is preferably co-extensive in area and position with the corresponding end of the ignition lead 20 in the rotor 14 (when the rotor 14 is in its firing position). The support frame 28, being of a non-ferromagnetic material, does not affect the magnetic circuits. It will be appreciated that other igniters, optical, percussion, etc., may also be used.

The housing 12 contains an output charge 18 designed to connect with and ignite the desired propellant, explosive or pyrotechnic. It may be seen that the output charge 18 communicates through the housing 12 to an opening directly adjacent the outer surface of the rotor 14, opposite the explosive column 26. It may be seen in FIGS. l-3 that there is no communication between the igniter l6 and the output charge 18 with the rotor 14 in its normal or safe condition. The solid body of the rotor 14 and the support frame 28 confine and block any output of the igniter 16 from reaching the output charge 18.

The rotor 14 (as well as part of its support frame 28) is closely surrounded by the coil 24. The coil 24 is of conventional construction, having a sufficient number of turns (e.g., 1400 turns of No. 40 wire) in a toroidal configuration to be able to overcome the low frictional forces on the rotor 14 with the application of a low battery voltage to the coil. The axis of rotation of the rotor 14 is perpendicular to the axis of the coil 24. The coil 24, when actuated, produces a magnetic field through the rotor 14 parallel the axis of the coil 24. The outer surface of the coil 24 is surrounded by a continuous shield 22 of soft magnetic sheet metal. For example, permalloy of 0.006 inches thickness. Thus, the magnetic shield 22 also surrounds and encloses the rotor 14, although spaced therefrom.

The rotor 14 is preferably entirely constructed as a solid cylinder of permanent magnetic material, for example Alnico. The rotor 14 is preferably magnetized, along a central radial axis as conventionally illustrated in FIGS. 1 3 by the symbol M and its associated arrows. It will be appreciated that a variable reluctance arrangement can be employed instead. The

' rotor 14 requires no mechanical support or connection other than conventional low friction bearings 30 on each side with which the rotor is rotatably mounted to the support frame 28. No other mechanical connection or restraint is required for the rotor 14. Of course additional indicators or switches may be provided for actuation by the rotor 14 to provide an external indication of the rotor position. Preferably the rotor is a solid balanced mass with its center of mass at the axis of rotation (the bearings 30) so that the rotor 14 is not moved by external forces. The rotor 14 may be small and lightweight. The thickness need only be sufficient to confine the ignition lead 20, and the diameter need only be sufficiently large to provide adequate separation between the igniter l6 and output charge 18. The strength of the magnetization of the rotor 14 need not be large as in the rotating of the rotor 14 by the application of magnetic fields thereto only the low frictional forces in the bearings 30 need be overcome. The rotor 14 may thus be rapidly rotated from its safe position to its armed position upon the application of the arming current to the coil 24. Eddy current effects are not utilized and do not affect the operation of the rotor 14.

The ignition lead 20 through the rotor 14 comprises a continuous enclosed passageway opening at opposite sides of the rotor 14 and containing a suitable explosive material. Suitable conventional secondary explosives such as RDX or PETN may be used, for example. When the rotor 14 is in its firing position one end of the ignition lead 20 overlies and is closely spaced from the explosive column 26 and output charge 18, respectfully, so as to provide a direct firing train or explosive column between the igniter 16 and the output charge 18. With the rotor 14 in its safe position as illustrated in FIGS. 1-3 the ignition lead 20 is at right angles to the path between the igniter and the output charge and communicates with neither, i.e., the ignition lead 20 is misaligned and provides a positive safety.

The initiator is maintained in its safe position without any mechanical restraints by the magnetic interaction of the rotor 14 with the magnetic shield 22. The magnetic field of the rotor 14 magnetically couples to the shield 22 to rotate the rotor to a position in which the magnetic air gap is a minimum, which is the safe position. Thus, it may be seen that the rotor 14 is continuously magnetically urged out of its armed position into the safe position, and is magnetically maintained in its safe position. Only when sufficient arming current is applied to the coil 24 to establish a second and stronger mag netic field will the rotor 14 be rotated out of its safe position. With the configuration of the initiator 10 the rotor 14 will move from the safe to the arm condition upon the application of current to the coil 24 irrespective of the polarity of the arming current or the magnetic polarity of the rotor 14. (The rotor 14 rotates 90.) The initiator 10 provides excellent security against accidental arming by electrical noise or spurious electrical signals, even if applied through the arming circuit. The rotor 14 is not moved by alternating currents or brief intermittent electrical signals applied to the coil 24 irrespective of their intensity.

The rotation of the rotor 14 from its safe position to its armed position is accomplished solely by the application of a DC arming signal to the coil 24. The coil 24 directly magnetically couples with the rotor to achieve the rotation and alignment in the firing position of the rotor 14 without any mechanical connection to the rotor. The rotor 14 will remain in its firing position, as shown in FIG. 4, as long as the arming signal is applied. As soon as the arming signal is removed the rotor 14 is rotated back into its safe position by the magnetic attraction of the rotor by the shield 22. The rotor 14 may be repeatedly armed or disarmed for test purposes without affecting its safety characteristics. The interaction of the magnetic field of the rotor 14 with the shield 22 continues to urge the rotor out of the armed position. However, the torque on the rotor due to this magnetic force is much less than the torque impressed on the rotor by the magnetic field of the coil 24. Thus, the magnetic field of the coil 24 readily overcomes the existing magnetic force to align the rotor 14 with the magnetic field of the coil 24.

A generally conventional safety firing circuit 32 is illustrated in FIG. 4 here. The firing circuit 32 incorporates a conventional double pole double throw relay 34 for a conventional firing and arm permit circuitry. It will be appreciated that this arrangement is not essential and that a simple initiator 10 can be provided with only an arm lead and fire lead (eliminating the relay and arm permit circuitry). However, it may be seen in FIGS. 1 and 2 that the initiator 10 readily provides for the integration of the firing circuit 32 therein, as the relay 34 may be mounted directly to the support frame 28 inside the housing 12. The return circuits (ground leads) have been eliminated in FIGS. 1 and 2 for purposes of clarity. Conventional grounding of return circuits at a common point is indicated in FIG. 4. Conventional electrical connectors and leads may be utilized to connect the initiator 10 to the external circuitry. As previously indicated all input circuits, both firing and arming, carry only low voltage, low power signals, unlike conventional exploding brid e wire circuitry.

It may be seen that there as been described herein an improved initiator which is simple, reliable and provides excellent safety against undesired ignition without requiring high voltage or high power circuitry or complex mechanical arrangements. The initiator may be manufactured at low cost in various forms. While the apparatus described herein is presently considered to be preferred, it is contemplated that further variations in modifications within the purview of those skilled in the art can be made herein. The following claims are intended to cover all such variations and modifications as fall within the true spirit and scope of the invention.

What is claimed is: l. A safe/arm initiator comprising: a housing; a permanent magnetic rotor rotatably mounted in said housing; said rotor having an ignition lead extending therethrough; an igniter in said housing adjacent said rotor; an output charge adjacent said rotor and spaced from said igniter; said ignition lead being operatively interposed between said igniter and said output charge upon the rotation of said rotor into an armed position; magnetic path means fixed in said housing around said rotor magnetically coupled to said rotor continuously magnetically urging said rotor out of said armed position; and a non-magnetic material field coil in said housing magnetically coupled to said rotor and excitable by an arming signal applied thereto to overcome said magnetic path means by a stronger electro magnetic force acting angularly thereto and magnetically rotate said rotor into said armed position; said rotor being magnetically rotated into and maintained in said armed position by the application of said arming signal to said field coil until said arming signal is removed; said rotor being magnetically rotated out of said armed position and maintained out of said armed position by said magnetic path means automatically upon the removal of said arming signal from said field coil. 

1. A safe/arm initiator comprising: a housing; a permanent magnetic rotor rotatably mounted in said housing; said rotor having an ignition lead extending therethrough; an igniter in said housing adjacent said rotor; an output charge adjacent said rotor and spaced from said igniter; said ignition lead being operatively interposed between said igniter and said output charge upon the rotation of said rotor into an armed position; magnetic path means fixed in said housing around said rotor magnetically coupled to said rotor continuously magnetically urging said rotor out of said armed position; and a non-magnetic material field coil in said housing magnetically coupled to said rotor and excitable by an arming signal applied thereto to overcome said magnetic path means by a stronger electro magnetic force acting angularly thereto and magnetically rotate said rotor into said armed position; said rotor being magnetically rotated into and maintained in said armed position by the application of said arming signal to said field coil until said arming signal is removed; said rotor being magnetically rotated out of said armed position and maintained out of said armed position by said magnetic path means automatically upon the removal of said arming signal from said field coil. 